#include<bits/stdc++.h>
#define db double
using namespace std;
const int N=1e5+5;
int n,vis[N][2];
db ans,ans1,ans2,a[N],b[N];
bool cmp(db x,db y){
	return x>y;
}
int main(){
	freopen("wager.in","r",stdin);
	freopen("wager.out","w",stdout);
	ios::sync_with_stdio(0);
	cin.tie(0);cout.tie(0);
	cin>>n;
	for(int i=1;i<=n;i++){
		cin>>a[i]>>b[i];
	}
	sort(a+1,a+1+n,cmp);
	sort(b+1,b+1+n,cmp);
	int i=1,j=1;
	while(i<=n&&j<=n){
		if(!vis[i][0]){
			ans1+=a[i];
		}
		if(!vis[j][1]){
			ans2+=b[j];
		}
		vis[i][0]=vis[j][1]=1;
		ans=max(min(ans1-db(i+j),ans2-db(i+j)),ans);
		if(ans1>=ans2) j++;
		else i++;
	}
	cout<<fixed<<setprecision(4)<<ans<<"\n";
	return 0;
}